1. Technical Field
The present invention relates to a fluid ejection device which ejects fluid at high speed, and more particularly to a fluid ejection device, a driving method of a fluid ejection device, and an operating instrument capable of controlling fluid ejection according to contact condition between an ejection target object and an ejection end.
2. Related Art
A fluid ejection device which opens or removes tissue of a living body by cutting has been proposed by the present inventors (see JP-A-2008-82202).
This fluid ejection device includes: a pulse generating unit which has a fluid chamber whose capacity is variable, inlet flow path and outlet flow path communicating with the fluid chamber, a capacity changing unit for changing the capacity of the fluid chamber according to supply of driving signals; a connection flow path which has one end communicating with the outlet flow path and the other end having a fluid ejection opening (nozzle) whose diameter is smaller than that of the outlet flow path; a connection flow pipe containing the connection flow path and having rigidity sufficient for transmitting pulse of fluid flowing from the fluid chamber to the fluid ejection opening; and a pressure generating unit which generates pressure for supplying fluid to the inlet flow path. The fluid ejection device supplies fluid to the inlet flow path with constant pressure produced by the pressure generating unit, and generates pulse by changing the capacity of the fluid chamber using the capacity changing unit to deliver fluid.
When the capacity of the fluid chamber of the fluid ejection device is not changed, fluid flows under the balanced condition between supply pressure produced by the pressure generating unit and fluid path resistance. In this condition, delivery of fluid from the nozzle is continuous at low speed, producing substantially no tissue cutting capability.
When the capacity of the fluid chamber is rapidly decreased, the pressure of the fluid chamber increases. In this condition, increase in the flow amount of fluid delivered from the outlet flow path is larger than decrease in the flow amount of fluid flowing into the fluid chamber from the inlet flow path. Thus, pulsed flow is generated in the connection flow path. This pressure change at the time of delivery is transmitted through the connection flow path pipe such that fluid can be ejected from the fluid ejection opening formed at the end of the nozzle at high speed.
By repeating this operation, fluid can be delivered by high-speed pulse jet. In this structure, starting and stopping at the speed of several msec. or lower can be achieved by contracting and expanding the fluid chamber using a piezoelectric element.
This technology is applicable to a fluid ejection device disclosed in another reference (see JP-A-2005-152127) proposed by the present inventors as ejection device requiring no pressure generating unit.
When the fluid ejection device in the related art discussed above is used as a water scalpel in an operation, the operation is performed with the nozzle almost closely attached to the affected part. Thus, when the nozzle ejecting fluid is separated from the affected part, liquid drops produced by the fluid ejection are scattered. In this case, there is a possibility that removed pieces of tissue containing cancer or the like are scattered around.